Calculate Mass of Iron Converted into Fe3O4 by Steam

To find the mass of iron ($\text{Fe}$) converted into magnetic iron oxide ($\text{Fe}_3\text{O}_4$), we start by writing the balanced chemical reaction between iron and steam ($\text{H}_2\text{O}$):

$3\text{Fe}(s) + 4\text{H}_2\text{O}(g) \rightarrow \text{Fe}_3\text{O}_4(s) + 4\text{H}_2(g)$

Step 1: Calculate the molar masses of the substances.

• Molar mass of steam ($\text{H}_2\text{O}$) = $2(1) + 16 = 18\text{ g mol}^{-1}$
• Molar mass of iron ($\text{Fe}$) = $56\text{ g mol}^{-1}$

Step 2: Calculate the number of moles of steam available. $\text{Moles of }\text{H}_2\text{O} = \frac{\text{Given mass}}{\text{Molar mass}} = \frac{18\text{ g}}{18\text{ g mol}^{-1}} = 1\text{ mol}$

Step 3: Determine the required moles of iron using stoichiometry. From the balanced chemical equation, $4\text{ moles}$ of $\text{H}_2\text{O}$ react completely with $3\text{ moles}$ of $\text{Fe}$.

Therefore, $1\text{ mole}$ of $\text{H}_2\text{O}$ will react with: $\text{Moles of }\text{Fe} = \frac{3}{4} \times 1\text{ mol} = 0.75\text{ mol}$

Step 4: Calculate the mass of iron consumed. $\text{Mass of }\text{Fe} = \text{Moles of }\text{Fe} \times \text{Molar mass of }\text{Fe}$ $\text{Mass of }\text{Fe} = 0.75\text{ mol} \times 56\text{ g mol}^{-1} = 42\text{ g}$

Thus, the mass of iron converted into $\text{Fe}_3\text{O}_4$ is $42\text{ g}$.

Correct Option: D